The present invention generally relates to a method for inhibiting the oxidation of polyunsaturated lipids using uniquely effective combinations of two or more polyamines, and the stabilized products obtained therefrom.
Recent trends in food processing and preparation include efforts to reduce the saturated fatty acid content of many foods in favor of unsaturated fatty acids. Among other things, the replacement of saturated fats in a diet with polyunsaturated fats can help to reduce cholesterol levels.
Omega-3 long chain polyunsaturated fatty acids. in particular, have been viewed as highly attractive potential additives for foods and dietary supplements. Omega-3 polyunsaturated fatty acids are found naturally in marine oils, and also in certain vegetable oils. Certain fish oils, such as capelin oil, cod liver oil, and menhaden oil, contain large amounts of highly unsaturated long chain fatty acids, such as eicosapentaenoic acid (EPA), docosahexaenoic (DHA), and eicosatetraenoic acid (arachidonic acid). EPA and DHA are omega-3 fatty acids. Many vegetable oils contain linoleic acid, an essential fatty acid, which is classified as an omega-6 fatty acid. However, unlike many other vegetable oils, flaxseed oil also contains significant amounts (generally about 55 to about 65 percent) alpha linolenic acid (ALA), which is another essential fatty acid. ALA also is an omega-3 fatty acid. Small amounts of ALA also can be found, for example, in walnut oil, canola oil, soybean oil, and black currant. The body metabolizes ALA, at least in part, into EPA, and, to a lesser extent, DHA and 3-series prostaglandins.
The omega-3 fatty acids obtained directly from fish oils (i.e., EPA and DHA) are thought to offer a wide range of possible nutritional and health benefits. These benefits include reductions in cholesterol levels, anti-thrombotic effects, anti-arthritic effects in joints, and enhancement of mental and visual acuity. ALA has been reported to be useful in lowering blood pressure, controlling inflammatory conditions, inhibiting autoimmune reactions, and protecting against cardiovascular disease.
While foods and dietary supplements prepared with such polyunsaturated fatty acids may be healthier, they also have an increased vulnerability to rancidity. Rancidity in lipids, such as unsaturated fatty acids, is associated with oxidation off-flavor development. The off-flavor development involves food deterioration affecting flavor, aroma, color, texture, and the nutritional value of the particular food. A primary source of off-flavor development in lipids, and consequently the products that contain them, is the chemical reaction of lipids with oxygen. The rate at which this oxidation reaction proceeds has generally been understood to be affected by factors such as temperature, degree of unsaturation of the lipids, oxygen level, ultraviolet light exposure, presence of trace amounts of pro-oxidant metals (such as iron, copper, or nickel), lipoxidase enzymes, and so forth.
From the standpoint of food oxidation, the relevant lipids are compounds containing unsaturated fatty acids. Hydroperoxides are the major initial reaction products of the oxidation of the unsaturated fatty acids. The hydroperoxides are unstable, highly reactive intermediates, which can be responsible for the off-flavor development themselves, or as they further decompose, they form volatile aldehydes or ketones responsible for strong unpleasant smell and taste. In addition, free radicals formed during oxidation of the unsaturated fatty acids may participate in the development of arteriosclerosis and other pernicious diseases in the consumer.
The susceptibility and rate of oxidation of the unsaturated fatty acids can rise dramatically as a function of increasing degree of unsaturation in particular. In this regard, EPA and DHA contains five and six double bonds, respectively. This high level of unsaturation renders the omega-3 fatty acid fish oils readily oxidizable. The natural instability of such fish oils gives rise to their unpleasant odor and unsavory flavor characteristics where oxidation of the fish oils has occurred, even after a relatively short period of storage time. The odor and flavor of rancid fish oils are strong and pungent. Consequently, elimination of these odors and tastes, once generated, has been difficult if not impossible. Moreover, the off-flavor odor or taste can be so malodorous that even a small level of rancidity in a fish oil-containing product can be negatively perceived by a consumer. Linolenic acid (ALA) derived from plant oils is also very susceptible to off-flavor development. Dietary supplements containing omega-3 oils often are packaged in dark, light-blocking containers in either encapsulated form; free liquid forms generally require chilled storage once opened. Despite such precautions, they still tend to have a strong fish-like flavor and/or smell. Consequently, it has been very difficult in the past to produce omega-3 fatty acid containing products or supplements having an extended shelf life.
Previous proposals or practices for addressing lipid oxidation include, for example, U.S. Pat. No. 4,975,290 which describe a method of inhibiting lipid oxidation in food products such as uncured meat and extruded food products using an aqueous solution of organic iron salt. U.S. Pat. No. 5,015,483 describes means for stabilizing oxidizable lipophilic components such as fish oils by encapsulation of the components in a lipidic bilayer of liposomes (preferably saturated phospholipids). U.S. Pat. No. 5,077,069 describes use of natural antioxidants including tocopherols, ascorbic acid, citric acid, and phospholipids, and optionally rosemary extract, for stabilizing polyunsaturated oils. U.S. Pat. No. 5,230,916 describes use of an ascorbic acid complex for stabilizing polyunsaturated oils. U.S. Pat. No. 5,304,679 describes a composition for inhibiting the enzymatic browning of foods and beverages by using certain resorcinol-derivatives in place of earlier enzymatic browning inhibitors such as sodium bisulfite. U.S. Pat. No. 5,891,491 describes use of certain dihydroxyquinoline compounds to extend the shelf life of products derived from mammals and fish fed a diet including such compounds. Also, EPO 0 209 509 describes protecting easily oxidizable compounds, especially polyunsaturated fatty acids, against oxidation, in which the anti-oxidant is a compound containing primary or secondary amino-groups linked to carbon in an aliphatic residue of a certain described formula. The antioxidants are specifically characterized therein as being either spermine or spermidine. Also, comparative reference is made to BHA (butylated hydroxyanisole) and TBHQ (tertiary butylhydroquinone) as anti-oxidants. Although not directed to anti-oxidants for lipids, Japanese Pat. Publ. Kokai No. 6-305956 describes a protein absorption enhancing agent containing a polyamine as the active component, and a nutrient composition containing the polyamine and food components such as artificial milk powder formulas. Spermine individually is characterized therein as being particularly effective as the polyamine active agent for the protein absorption enhancing function.
Despite these prior proposals, there still remains a need for commercially viable approaches to fully realize the health and nutritional benefits of foods or supplements containing omega-3 oils and other beneficial polyunsaturated fatty acids. In particular, there remains a need for advanced, cost-effective and safe measures which can significantly impede the rates at which such polyunsaturated fatty acids and products containing them become rancid. The present invention fulfills these needs, as well as other needs and objectives, by a method for processing unsaturated lipids by contacting them with a uniquely effective combination of tow or more polyamines.
The present invention provides a method for treating polyunsaturated lipids by blending them with at least two different polyamines in amounts effective to induce a unique inhibitory effect on the rate of oxidative rancidity of the polyunsaturated lipids. The polyunsaturated lipids processed according to this invention have a significantly reduced rate of off-flavor development, which translates into increased shelf-life for the polyunsaturated lipids and any products containing them.
The effective amounts of the different polyamines used in combination with the polyunsaturated lipid in the practice of this invention can vary depending on the types of the polyamines and polyunsaturated lipid involved in the combination, as long as the respective amounts of the different polyamines are sufficient, in combination, to reduce the rate of oxidative rancidity of the polyunsaturated lipid. As demonstrated by experimental data discussed in more detail below, this reduction in the rate of oxidative rancidity is manifested as a greater increase in the oxidative stability of the polyunsaturated lipid or composition containing the lipid blended with the combination of polyamines according to the invention, as compared to the same lipid treated with a single polyamine of the combination at the same overall polyamine concentration. For purposes herein, the oxidative stability parameter is measured as an oil stability index (OSI) value at a given temperature. The OSI is an accelerated rancidity test, described in more detail hereinafter, that measures the rate of oxidation of a oil or fat. It is expressed as a numerical index value. The higher the index value, at a given temperature, the more stable the oil or product containing same is to oxidation. The OSI value observed for polyunsaturated lipids treated according to the invention with the combination of different polyamines is significantly greater than that observed for the same lipid except as treated with only one of the polyamines at the same overall concentration level.
Generally, the practice of this invention allows the OSI110 value (i.e., the OSI value as measured at 110xc2x0 C.) of a polyunsaturated lipid treated with a combined amount of two or more polyamines according to the invention to increase, on average, about two fold or more, preferably about three fold or more, and more preferably about five fold or more, than the OSI110 value of the same polyunsaturated lipid where treated with an equivalent concentration of either of polyamine ingredients alone. As a result, the combination of the polyamines used in treating polyunsaturated lipids according to this invention can effectively retard oxidation and off-flavor development in polyunsaturated lipids.
To accomplish this advantageous effect of the invention, each of the different polyamine ingredients is generally mixed with polyunsaturated lipid in an amount of at least about 0.25 millimoles (mM), preferably at least about 0.5 mM, and more preferably at least about 1.5 mM. Generally, the total amount of the two or more polyamines is about 0.5 to about 9 mM, preferably about 1 to about 6 mM, and more preferably about 1.5 to about 3 mM.
The polyamines suitable for treating the polyunsaturated lipids according to this invention, generally include linear aliphatic polyamines. The different polyamines, which are combined together, can be generally represented by the general formula:
H2Nxe2x80x94[(CH2)pxe2x80x94(NH)qxe2x80x94(CH2)rxe2x80x94(NH)sxe2x80x94(CH2)t]uxe2x80x94NH2
wherein u is an integer of 1 to 5; p, r, and t independently are integers of 0 to 8, with the proviso that at least one of p, r, and t is greater than or equal to 2; wherein q and s independently are 0 or 1, with the proviso that at least one of u, p, r, t, q, and s has a different integer value in the first polyamine than in the second polyamine.
In a preferred aspect of the invention, the combination of polyamines includes spermine used in combination with spermidine, putrescine, or mixtures thereof. These linear, aliphatic polyamines are biocompatible, naturally occurring polyamines which are well-suited for food products and dietary supplement applications. Generally the polyunsaturated lipid is blended with a polyamine composition containing about 10 percent to about 90 percent of spermine and about 10 percent to about 90 percent of the second polyamine; preferably, the polyamine composition contains about 40 to about 60 percent of spermine and about 40 percent to about 60 percent of the second polyamine. In other words, the ratio of spermine to the second polyamine is generally about 1:9 to about 9:1 and preferably about 2:3 to about 3:2. In a preferred aspect of the invention, the polyunsaturated lipid treated according to the invention is a polyunsaturated fatty acid, and more preferably is an omega-3 fatty acid.
In one advantageous aspect of the invention, the present invention fulfills a vital commercial need for rancidity-inhibiting measures suited for omega-3 fatty acids, in which the protection measures are based on edible (food-friendly) additives, namely, the use of combined polyamines as described herein. Suitable omega-3 fatty acids include eicosatetraenoic acid (EPA), docosahexaenoic acid (DHA), alpha linolenic acid (ALA), and mixtures thereof. The present invention permits the considerable potential health benefits available in fish oils and vegetable oils that contain omega-3 fatty acids to be more fully accessed, while significantly increasing the shelf-life of such products. Moreover, due to the increased shelf-life attained, the omega-3 fatty acid containing oils processed according to the invention can be used as substitutes for saturated fats in food products or as a nutritional supplement taken separately or as added to foods or beverages.
Although the polyamine-treated polyunsaturated lipids prepared according to this invention are suitable for food products in particular, they are not necessarily limited thereto. They also could be used in other applications involving polyunsaturated lipid content including, for example, cosmetics, medicinal or cosmetic topical ointments, medicinal or cosmetic topical lotions, medicinal or cosmetic topical creams, personal care products, and the like.